Abstract
BackgroundAlthough the benefits of physical activity in preventing chronic medical conditions are well established, its impacts on infectious diseases, and seasonal influenza in particular, are less clearly defined. We examined the association between physical activity and influenza-coded outpatient visits, as a proxy for influenza infection.Methodology/Principal FindingsWe conducted a cohort study of Ontario respondents to Statistics Canada’s population health surveys over 12 influenza seasons. We assessed physical activity levels through survey responses, and influenza-coded physician office and emergency department visits through physician billing claims. We used logistic regression to estimate the risk of influenza-coded outpatient visits during influenza seasons. The cohort comprised 114,364 survey respondents who contributed 357,466 person-influenza seasons of observation. Compared to inactive individuals, moderately active (OR 0.83; 95% CI 0.74–0.94) and active (OR 0.87; 95% CI 0.77–0.98) individuals were less likely to experience an influenza-coded visit. Stratifying by age, the protective effect of physical activity remained significant for individuals <65 years (active OR 0.86; 95% CI 0.75–0.98, moderately active: OR 0.85; 95% CI 0.74–0.97) but not for individuals ≥65 years. The main limitations of this study were the use of influenza-coded outpatient visits rather than laboratory-confirmed influenza as the outcome measure, the reliance on self-report for assessing physical activity and various covariates, and the observational study design.Conclusion/SignificanceModerate to high amounts of physical activity may be associated with reduced risk of influenza for individuals <65 years. Future research should use laboratory-confirmed influenza outcomes to confirm the association between physical activity and influenza.
Highlights
The protective effects of physical activity against chronic diseases such as coronary artery disease, hypertension, noninsulin-dependent diabetes mellitus, osteoporosis, colon cancer, anxiety, and depression are well established [1]
Previous studies have mainly examined the relationship between physical activity and upper respiratory tract infections (URTIs), and have focused on small samples of athletes rather than the general population [4]
The association has been described as a J-shaped curve [5,6]; strenuous exercise such as marathon running can increase susceptibility to URTIs [7,8], while moderate physical activity can reduce the risk [9,10,11,12]
Summary
The protective effects of physical activity against chronic diseases such as coronary artery disease, hypertension, noninsulin-dependent diabetes mellitus, osteoporosis, colon cancer, anxiety, and depression are well established [1]. Little is known about the potentially protective effects of physical activity on infections, seasonal influenza, which continues to cause substantial morbidity and mortality [2,3]. Previous studies have mainly examined the relationship between physical activity and upper respiratory tract infections (URTIs), and have focused on small samples of athletes rather than the general population [4]. The association has been described as a J-shaped curve [5,6]; strenuous exercise such as marathon running can increase susceptibility to URTIs [7,8], while moderate physical activity can reduce the risk [9,10,11,12]. We examined the association between physical activity and influenza-coded outpatient visits, as a proxy for influenza infection
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